Sweep the porch and mop it with an appropriate cleanser for the floor material.
Mark off the rug's borders with low-tack painter's tape. Use a carpenter's square and yardstick to ensure that your corners are 90 degrees and your lines are even with the surrounding walls.
Apply several more layers of painter's tape outside of the first, creating a tape border at least 6 inches thick around the area you intend to paint.
Apply a thin coat of Spackle with a putty knife to fill in any texture in the porch floor. If your porch is smooth, skip this and the next step.
Sand the Spackle smooth with 120-grit sandpaper and an electric sander, and then again with 220-grit sandpaper. Wipe it with tack cloth to remove the sanding dust.
Apply two coats of exterior primer with a paint roller, allowing each coat to dry completely.
Apply two coats of your main paint color for the rug. The paint should be rated for heavy foot traffic.
Paint designs and patterns onto the rug, either freehand or through the use of stencils.
Allow all of the paint to dry.
Run a razor blade along the inner edge of the painter's tape to ensure that it does not peel up any of the paint.
Remove the painter's tape.
Paint small details, such as tassels, onto the floor around the rug if desired.
Apply two coats of matte sealer onto the rug and surrounding area with a paint roller. Allow the sealer to dry for the time recommended on the container before walking on the painted rug.